The present invention relates to a Pisum sativum variety that contains a recessive gene that produces highly wrinkled seed having a low starch content. Additionally, the present invention relates to nucleotide sequences for said recessive gene and methods for using said nucleotide sequences in site-specific recombination.
The garden pea (Pisum sativum L.) is a commercially important food crop and the immature seed of the garden pea (xe2x80x9cpeasxe2x80x9d) are widely consumed. There are a large number of genes that affect starch or carbohydrate synthesis in peas. The first reported and best described gene is the r gene (see White, O. E., Proceedings of the American Philosophical Society, 56: 487-588). The r mutant is believed to have occurred spontaneously at the beginning of the seventeenth century (see Lamprecht, H., Agri. Hortique Genetica 14: 1-4 (1956)) and its mature, dry seed has a wrinkled appearance (hence xe2x80x9crxe2x80x9d, derived from the Latin, rugosus meaning xe2x80x9cwrinkled or shriveledxe2x80x9d). Wrinkling of mature seed was one of the characteristics used by Mendel in experiments which led him to formulate his laws of inheritance. (see Mendel, G., Verhandlungen des Naturforschenden Vereinds in Brxc3xcnn 4: 3-47 (1865)).
Recessive alleles at the r locus not only have a profound effect on the shape of the seed, but also have numerous effects at all levels of seed development. Wang, T. L., et al., Seed Science Research 1:3-14 (1991). Specifically, seeds of the r mutant contain a lower proportion of starch than the wildtype (about 30% dry weight as opposed to about 50%) with the starch composition being altered to contain a higher proportion of amylose and a small proportion of amylopectin (with about 70% of dry weight of the starch of mutant seeds being amylose as opposed to 38% of the wildtype starch). For a long period of time, the molecular basis of the mutation was not clear. The difference in the level and composition of starch in the seed led several investigators to examine the various enzymes of starch biosynthesis. Id. Early studies indicated that the mutation was likely to be in the starch branching enzyme and this was confirmed when it was shown, using a pair of lines near-isogenic except for genes at the r locus that rr embryos lacked one form of the starch-branching enzyme, which is frequently referred to as xe2x80x9cSBE1xe2x80x9d. Subsequently, it was shown that the mutant was caused by a transposon-like insertion in the gene encoding SBE1. Id.
A second recessive rugosus locus termed xe2x80x9crbxe2x80x9d is also known. Mutants homozygous recessive at this locus exhibit a wrinkled seed phenotype similar to that of rr plants. However, the amount of starch and its composition in the rb mutant are different than that of the r mutant. Specifically, seed of the r mutant contains about 30% dry weight of starch, of which about 70% is amylose. Seed of the rb mutant contains about 36% dry weight of starch, of which about 23% is amylose. The rb mutation has been found to result in reduced activity in the enzyme ADP glucose pyrophosphorylase. Purification of the enzyme and western blot experiments have revealed the absence of one of the four polypeptide subunits present in the wildtype enzyme.
WO 98/01574 describes Pisum sativum varieties which contain a mutation referred to as xe2x80x9crug3xe2x80x9d. Plants containing the rug-3 mutation produce wrinkled seeds having low levels of starch, high levels of sucrose, as well as a high protein and lipid content. The rug-3 mutation has been found to be associated with a reduction in the activity of the enzyme plastid phosphoglucomutase (hereinafter xe2x80x9cPGMxe2x80x9d). According to WO 98/01574, pea seeds containing the rug-3 mutation have a sucrose content of greater than 6% by weight of the total weight of the seed as harvested at a tenderometer reading exceeding 120 tenderometer units.
The rug-3 mutation described in WO 98/01574 was induced via a mutagenesis program. Twenty thousand phenotypically round genetically wildtype (RR) seeds (referred to as xe2x80x9cM1xe2x80x9d seed) were treated with ethyl methanesulphonate or N-methyl-N-nitrosourea, which are known mutagens. M1 seed gave rise to M1 plants bearing M2 seed. M2 seed gave rise to M2 plants bearing M3 seed. M3 seeds were analyzed for storage product content. Seeds which exhibited a wrinkled appearance were selected from the M3 generation. These seeds were found to contain a wide range of starch, from 0-60% as a proportion of the dry weight of the mature seed. Within the starch of these seeds, the amylose content ranged from 0-80%. Also, the lipid content of the peas ranged from about 1 to about 8% of the dry weight and protein ranged from about 24 to about 48%. WO 98/01574 does not contain any information characterizing the rug-3 mutant except to describe how this mutation was induced via a mutagen program. Additionally, WO 98/01574 does not contain any information that distinguishes the DNA sequence of the rug-3 mutant from that of the wildtype and contains no information on effects on alcohol insoluble solids content.
WO 98/01574 also describes the isolation and characterization of the nucleotide sequence for wildtype pea plastid phosphoglucomutase. According to WO 98/01574, this nucleotide sequence can be introduced into a plant via recombinant DNA technology to produce transgenic plants in which the plastid PGM gene expression is down regulated or inactivated in developing seeds.
Sweetness in peas, associated with increased sugar content, is generally prized by consumers, who perceive that sweeter peas have a better flavor. Thereupon, because peas are such an important food crop, there is a need in the art for peas having an increased sweetness.
The present invention relates to a new variety of Pisum sativum, which is resistant to Fusarium Wilt Fungus and Powdery Mildew Fungus and which contains within its genome, a homozygous recessive gene, referred to as the bsg gene. It has been determined that the bsg gene contains a mutation in an intron in a 3xe2x80x2 splice site of the gene. More specifically, the bsg gene has the genomic nucleotide sequence shown in Sequence ID NO:1 and contains a mutation at nucleotide 1548 at the 3xe2x80x2 splice site dinucleotide AG, where nucleotide A is replaced with nucleotide T.
A Pisum sativum variety that contains the bsg gene within its genome produces peas (known in the art as immature seeds) which exhibit a lower level of starch, an elevated level of sucrose and a decreased level of alcohol insoluble solids when compared with peas produced from a Pisum sativum variety that does not contain the bsg gene homozygous within its genome.
Additionally, the present invention contemplates a Pisum sativum variety which contains a homozygous bsg gene within its genome. The bsg gene has the nucleotide sequence shown in SEQ ID NO:1 and contains a mutation in an intron at nucleotide 1548 at the 3xe2x80x2 splice site dinucleotide AG, where nucleotide A is replaced with nucleotide T.
The peas of the present invention contain from about 6.0 to about 7.5 percent fresh weight of sucrose when measured at a tenderometer value of from about 90 to about 110 and from about 6.5 to about 8.0 percent by weight of alcohol insoluble solids when measured at a tenderometer value of about 105. Moreover, the peas of the present invention contain from about 5 to about 30 percent fresh weight more sucrose than peas produced from a Pisum sativum variety that does not contain the bsg gene homozygous within its genome. Additionally, the peas of the present invention exhibit twenty (20) percent less alcohol insoluble solids when compared with peas from a Pisum sativum that does not contain the bsg gene homozygous within its genome.
Additionally, the present invention relates to a process for producing peas of a Pisum sativum variety that contain higher levels of sucrose and lower levels of alcohol insoluble solids than peas from a Pisum sativum variety that does not contain the bsg gene homozygous within its genome. The said process involves crossing a Pisum sativum variety or line that contains the bsg gene homozygous within its genome with a second Pisum sativum variety or line that contains the bsg gene homozygous within its genome, collecting the resulting mature seeds, planting the mature seeds, growing the mature seeds into Pisum sativum plants, selecting Pisum sativum plants with desirable phenotypic traits; allowing the plants to self-pollinate until a uniform line is produced, allowing the Pisum sativum line to self-pollinate, selecting plants with desirable phenotypes and collecting the resulting peas (which are also referred to as xe2x80x9cmature seedsxe2x80x9d).
In another embodiment, the process involves crossing a Pisum sativum variety or line that contains the bsg gene homozygous within its genome with a second Pisum sativum variety or line which does not contain the bsg gene within its genome, collecting dry, mature seeds, planting the collected dry, mature seeds, growing the mature seeds into Pisum sativum plants, allowing the plants to self-pollinate, collecting the resulting dry, mature seeds, selecting highly wrinkled mature seeds that do not contain organized starch grains and which do not stain purple when treated with a solution of iodine and potassium iodide, planting said highly wrinkled mature seeds, growing the mature seeds into Pisum sativum plants, selecting plants with desirable phenotypic traits, allowing the plants to self-pollinate until a uniform Pisum sativum line is produced, allowing the Pisum sativum line selected to self-pollinate, and collecting the resulting peas. The Pisum sativum variety or line that does not contain the bsg gene within its genome can contain any combination of the genes such as the r, rb, R or Rb homozygous within its genome. The peas produced by the process of the present invention contain from about 6.0 to about 7.5 percent fresh weight of sucrose when measured at a tenderometer value of from about 90 to about 110 and from about 6.5 to about 8.0 percent by weight of alcohol insoluble solids when measured at a tenderometer value of about 105.
The present invention also contemplates a process of producing highly wrinkled mature seed of a Pisum sativum variety that contains the bsg gene within its genome. In one embodiment the process involves crossing a Pisum sativum variety or line that contains the bsg gene within its genome with a second Pisum sativum variety or line that contains the bsg gene within its genome and collecting the resulting mature seeds.
In another embodiment, the process involves crossing a Pisum sativum variety or line that contains the bsg gene within its genome with a Pisum sativum variety or line that does not contain the bsg gene within its genome, collecting mature seeds, planting the collected mature seeds, growing the mature seeds into Pisum sativum plants, allowing the plants to self-pollinate, collecting mature seeds, selecting highly wrinkled seeds that do not contain organized starch grains, planting said mature seeds and growing the seeds into Pisum sativum plants, selecting plants with desirable phenotypic traits, allowing the plants to self-pollinate until a uniform Pisum sativum line is produced, allowing the Pisum sativum line to self-pollinate and collecting the mature seeds.
The present invention also contemplates Pisum sativum varieties grown from the mature seed described above and peas harvested from said varieties.
In another embodiment, the present invention contemplates a DNA molecule containing a nucleotide sequence which encodes plastid phosphoglucomutase, where the nucleotide sequence contains at least one mutation in an intron. The mutation in the intron prevents the excision of the intron from a primary transcript during post-transcriptional modification of the transcript and produces at least one aberrant mRNA for translation. Preferably, the mutation is a mutation in a 3xe2x80x2 splice site in the intron. Most preferably, the mutation is in a dinucleotide AG, where the nucleotide A is replaced by nucleotide T. This DNA molecule can be isolated and purified and inserted into an expression vector containing the DNA molecule, a promoter and a polyadenylation signal. In this vector, the promoter is operably linked to the DNA molecule and the DNA molecule is operably linked to the polyadenylation signal. The promoter may be the cauliflower mosaic virus 35S promoter and the polyadenylation signal may be the polyadenylation signal of the cauliflower mosaic 35S gene. Bacterial cells, such as Agrobacterium tumefaciens and Agrobacterium rhizogenes cells, and plant cells may be transformed with this vector.
In yet another embodiment, the present invention relates to a plant which contains a gene encoding plastid phosphoglucomutase within its genome, where the gene contains at least one mutation in an intron. The mutation in the intron prevents the excision of the intron from a primary transcript during post-transcriptional modification of the transcript and produces at least one aberrant mRNA for translation. The plant containing such a mutated gene may be a monocot or a dicot. Preferably, the mutation is a mutation in a 3xe2x80x2 splice site in the intron. Most preferably, the mutation is in a dinucleotide AG, where the nucleotide A is replaced by nucleotide T.
In yet another embodiment, the present invention contemplates an isolated and purified DNA molecule having the nucleotide sequence shown in SEQ ID NO:1 as well as an expression vector containing this DNA molecule, a promoter and a polyadenylation signal. In this vector, the promoter is operably linked to the DNA molecule and the DNA molecule is operably linked to the polyadenylation signal. The promoter may be the cauliflower mosaic virus 35S promoter and the polyadenylation signal may be the polyadenylation signal of the cauliflower mosaic 35S gene. Bacterial cells, such as Agrobacterium tumefaciens and Agrobacterium rhizogenes cells, and plant cells may be transformed with this vector.
Finally, in yet another embodiment, the present invention contemplates a method of altering the level of plastid phosphoglucomutase expressed in a plant. The method involves transforming plant cells with a vector. The vector contains a promoter, a polyadenylation signal and DNA molecule having either (1) the nucleotide sequence of SEQ ID NO:1; or (2) a nucleotide sequence encoding plastid phosphoglucomutase where the nucleotide sequence contains at least one nucleotide which prevents the excision of at least one intron from a primary transcript during post-transcriptional modification of the transcript and which produces at least one aberrant mRNA for translation. The promoter is operably linked to the DNA molecule and the DNA molecule is operably linked to the polyadenylation signal.
The second step of the method involves regenerating plant cells to provide a differentiated plant. The final step of the method involves identifying a transformed plant having an altered level of plastid phosphoglucomutase expressed in that plant.